Mortise chisel setup

[Meatwad]

I wanted to ask you guys and girls that use a mortise chisels, are your chisels square all the way around? I thought they were supposed to be. Like a perfect rectangular piece of steel. I'm asking because I decided to buy some Narex mortise chisels after hearing good feedback on them. So far they've been good to use but I noticed today that they are not square. But this appears to be intentional because all of them are off to the same degree.

[Tom King]

Mine are a trapezoid shape.  I expect it would cost a lot more to produce perfectly square ones, and the clearance on the sides gives you some steerage capability.

[Meatwad]

Mine are trapezoid, too. I figured there was some good reason for this.

[JohnG]

They need to have some relief angle or else they’ll be a pain to use and tear up the inside of the mortise. They are much bigger and beefier to hold up to the heavier blows and prying out chips, but you don’t really want the sides to be in contact with the inside of the mortise. 

[Botch]

Mine are square, so maybe its an old-tool thing.  

[wtnhighlander]

So long as the cutting edge is wider than the heel of the bevel, you should be good. 

[Chestnut]

My Narex are trapezoids with the cutting edge side being the wider part. I think they come both ways square and tapered but for me personally i never make mortises the exact width as my chisel so it doesn't really much matter.

[Botch]

Ran across this Raymond Blackburn video this afternoon, and he talked about the difference between sash mortise chisels and registered mortise chisels; thought that might be the difference but no, both of his appear to be square all the way around.